The present invention relates to a high throughput screening (HTS) method, array assembly and system. Particularly, it relates to a method, assembly and system to identify a chemical stripping or cleaning solution.
A typical gas turbine engine includes a compressor, a combustor and a turbine. Gases flow axially through the engine. Compressed gases emerging from the compressor are mixed with fuel and burned in the combustor. Hot products of combustion emerge from the combustor at high pressure and enter the turbine where thrust is produced to propel the engine and to drive the turbine, which in turn drives the compressor.
The compressor and the turbine include alternating rows of rotating and stationary coated airfoils. High temperature combustion gases degrade the coatings through either hot corrosion or oxidation. Gases that circulate through the airfoils, particularly during operation on the ground, also include particles of sand, dust, oxides of calcium, magnesium, aluminum, silicon and mixtures that have been ingested by the engine. The oxides can combine to form particularly deleterious calcium-magnesium-aluminum-silicon-oxide systems (Caxe2x80x94Mgxe2x80x94Alxe2x80x94Sixe2x80x94O), referred to as CMAS. These contaminants can be in a molten state and can infiltrate pores and openings in engine parts that can lead to crack formation and part failure. Other contaminants may include iron and nickel oxides, sodium vanadates, sodium sulfates, sodium phosphates and the like.
Consequently, gas turbine components such as an airfoil must be periodically repaired by removing degraded coatings, mechanically repairing the airfoil and recoating the airfoil surface. Removal of the degraded coating can be accomplished through one or more chemical stripping or cleaning immersions. Repair of turbine engine parts can also involve cleaning cracks, crevices and surfaces to completely remove CMAS and other oxides, organic and inorganic impurities and dirt prior to alloy filling and brazing. A typical repair process consists sequentially of a dirt clean, coating strip, then a fluoride ion cleaning (FIC) or etching prior to weld/braze repair.
Current cleaning/stripping solutions are not as effective and selective as desired. Also, new stripping solutions must often be developed when new base metal airfoils are developed or when the airfoils are provided with new coatings. Typically, xe2x80x9cone-at-a-timexe2x80x9d experiments are used to identify a new solution. In these experiments, scrapped engine-run airfoil pieces are placed in a beaker of solution and immersed in a hot water bath. The solution can be evaluated for stripping or cleaning effectiveness first by visual inspection and then by cross-sectional microscopy of cut and polished pieces. This process is time consuming. Sometimes, several months of work is involved to screen a few dozen solutions at most and then to optimize one promising solution. Part-to-part and intrapart coating variability can complicate the evaluation process. The stripping of a solution on a different cut part piece can be difficult to determine from sample piece to sample piece. This can result in elimination of a promising solution too early in the screening process. There is a need for a method to rapidly and efficiently screen large numbers of chemical solutions for stripping or cleaning of an airfoil.
The invention incorporates a combinatorial chemistry approach to screening and optimizing solution mixtures for chemical stripping or cleaning of a gas turbine component coating. The method comprises selecting a gas turbine component chemical stripping or cleaning solution by combinatorial high throughput screening (CHTS).
In another embodiment, the invention relates to a method, comprising assembling a mask onto a test substrate to define a well array on the test substrate, establishing a combinatorial library of candidate liquid reactants by depositing a candidate liquid reactant into each well of the array in contact with a region of the substrate, effecting reaction of each candidate liquid reactant with the substrate and evaluating each region of the substrate to select a best reactant from among the candidate liquid reactants.
In another embodiment, the invention relates to a high throughput screening well array assembly. The assembly comprises (A) a metal substrate and (B) a mask that defines an array of wells on the substrate.
In still another embodiment, the invention relates to a combinatorial high throughput screening system. The system includes a well array assembly comprising (A) a metal test substrate and (B) a mask that defines an array of wells on the substrate and a reaction vessel to receive the well array assembly.